递归代码
int binary_search(int arr[],int left,int right,int key){if (left>right){//区间无效return -1;}int mid=left+(right-left)/2; //直接平均可能会溢出if(arr[mid]==key){return mid;}else if(key>arr[mid]){return binary_search(arr,mid+1,right,key); //右半区间继续查找}else{return binary_search(arr,left,mid-1,key); //左半区间继续查找}
}
循环代码
//代码中 arr 表示数组，left 表示区间左边界， right 表示区间右边界，mid 表示中间位置
int binary_search(int arr[],int left,int right,int key){int ret=-1;//未搜索到数据返回-1int mid;//中间位置while(left<=right){//只要区间有效就继续mid=left+(right-left)/2; //直接平均可能会溢出if(arr[mid]==key){ret=mid;//找到break; }else if(key>arr[mid]){//右半区间继续查找left=mid+1;}else{right=mid-1; //左半区间继续查找}}return ret; // 返回结果
}
1
#include<iostream>
using namespace std;
int main(){int a[5]={1,2,2,3,4};int n;cin>>n;int l=0,r=4;int m;while(l<=r){m=l+(r-l)/2;if(a[m]>=n){r=m-1;}else{l=m+1;}if(a[l]==n){cout<<l;return 0;}}cout<<-1;
}
2
#include<iostream>
using namespace std;
int main(){int a[5]={1,2,2,3,4};int n;cin>>n;int l=0,r=4;int m;while(l<=r){m=l+(r-l)/2;if(a[m]>n){r=m-1;}else{l=m+1;}if(a[r]==n){cout<<r;return 0;}}cout<<-1;
}
3
#include<iostream>
using namespace std;
int main(){int a[9]={1,4,5,8,10,10,12,13,15};int n;cin>>n;int l=0,r=8;int m;while(l<=r){m=l+(r-l)/2;if(a[m]>=n){r=m-1;}else{l=m+1;}if(a[l]>=n){cout<<l;return 0;}}cout<<-1;
}
4
#include<iostream>
using namespace std;
int main(){int a[9]={1,4,5,8,10,10,12,13,15};int n;cin>>n;int l=0,r=8;int m;while(l<=r){m=l+(r-l)/2;if(a[m]>n){r=m-1;}else{l=m+1;}if(a[r]<=n){cout<<r;return 0;}}cout<<-1;
}
